Power semiconductor modules such as those known from DE 199 42 915 A1 or DE 101 42 971 A1 have an insulating and thermally conductive mount (substrate) and one or more power semiconductor elements which are arranged on it. These are electrically connected to one another and to contact surfaces or contact elements via metallic conductor tracks which are formed on the upper face of the substrate. The lower face of the substrate, which is likewise metallic and, for example, is copper-coated, is pressed against a heat sink by pressure pieces. The heat sink is used to dissipate the heat which occurs during operation of the power semiconductor module. The power semiconductor modules as described above are frequently referred to as modules without base plates, since there is no intermediate metal plate between the substrate and the heat sink.
When using power modules without a base plate, it is necessary to press the ceramic firmly against the heat sink, since, in contrast to modules with a base plate, there is no mechanically provided heat transfer (metallic base plate). However, previous power semiconductor modules without base plates have been subject to the problem of providing a good thermal contact without in the process damaging the bonding connections which lead away from the semiconductor elements and are provided for making further contact. Owing to the bonding wires, it is not possible to press directly onto the chips in order to achieve the best possible thermal contact between the heat sources (power semiconductor components) and, through the substrate, to the heat sink. The requirement for an adequate thermal contact with the heat sink and the fact that pressure can be exerted on the substrate only at specific points frequently lead to considerable restrictions in the use of such power semiconductor modules.
In the known power semiconductor modules, points are kept free in the area surrounding the semiconductor components on the substrate, at which pressure is applied to the substrate by means of stamps or spring contacts. In this case, small stamps, pins, etc. press onto the substrate. Since the free area is, however, restricted, an optimum must therefore always be found between the electrically usable area and the area which is required for fitting the pressure contact surfaces. The disadvantage in this case is the area required for the pressure points and the fact that pressure cannot be applied directly at the actual points which require good thermal contact, since they are provided with bonding wires. DE 199 03 875 discloses an arrangement in which a specific form of pressure contact is provided instead of bonding wires. However, this is very complex, is also subject to defects in certain applications, and can be used only for a limited range of applications.